Adjustable flow-combining restrictor for hydraulic excavator dual pump circuit

Abstract

An oil hydraulic circuit for a hydraulic shovel with which a composite operation can be performed readily and smoothly without special skill in operation of the hydraulic shovel. The oil hydraulic circuit comprises a first actuator which can operate with pressure oil from a predetermined one or both of a pair of hydraulic directional control valve sets, a second actuator which operates only with pressure oil from the other hydraulic directional control valve set, a proportional changing over device interposed intermediately in a pipe line communicating the other hydraulic directional control valve set with a first actuator for adjusting the maximum meter-in opening value to the first actuator in response to a magnitude of a signal received at a signal receiving portion of the proportional changing over device, and a controller for arbitrarily adjusting the signal to be supplied to the signal receiving portion of the proportional changing over device.

What is claimed is: 
     
       1. An oil hydraulic circuit for a hydraulic shovel comprising: first and second hydraulic directional control valve sets, each of said first and second hydraulic directional control valve sets being adapted to receive a supply of pressure oil from first and second individual main pumps;   a first actuator which operates at a low speed with pressure oil from a first hydraulic directional control valve belonging to one of said first and second hydraulic directional control valve sets and which operates with pressure oil from said first hydraulic directional control valve belonging to said one of said first and second hydraulic directional control valve sets and also from a second hydraulic directional control valve belonging to the other of said first and second hydraulic directional control valve sets;   a second actuator which operates only with pressure oil from said second hydraulic directional control valve belonging to said other of said first and second hydraulic directional control valve sets;   a proportional changing over means having a signal receiving portion, said proportional changing over means being interposed intermediately in a pipe line communicating said other of said first and second hydraulic directional control valve sets with said first actuator for selectively communicating, throttling and cutting off fluid flow to said first actuator for adjusting a maximum meter-in opening value to said first actuator in response to a magnitude of a signal received at said signal receiving portion of said proportional changing over means; and   a controller for arbitrarily adjusting the signal to be supplied to said signal receiving portion of said proportional changing over means.   
     
     
       2. An oil hydraulic circuit for a hydraulic shovel according to claim 1, wherein said controller is provided in the neighborhood of an operator's seat in a cage of said hydraulic shovel. 
     
     
       3. An oil hydraulic circuit for a hydraulic shovel according to claim 1, further comprising a proportional signal converting device for converting said signal from said controller into a signal in the form of a hydraulic pressure.